The Brumbies will take on the Bulls in Pretoria next week after a conversion miss saw them edge the Cheetahs by a 15-13 margin in Canberra on Sunday.
It couldn't have been closer as Riaan Smit's last minute touchline conversion attempt from Rayno Benjamin's try bounced back off the post and with it went the Cheetahs' dreams of a semi-final.
Instead, it will be a Bulls versus Brumbies clash at Loftus Versfeld after what was a gripping 80 minutes that was up at Test match intensity.
The Brumbies began the contest in sprightly fashion and it was clear which team had not played since July 6, with the Cheetahs struggling to get up to pace in the early sparring. In fact the visitors came close to losing a man in the first minute when the powerful number eight, Philip van der Walt, went down with a knee issue.
He, like the Cheetahs, recovered to compete in an evenly matched first-half, with both teams showing plenty with and without the ball.
Christian Lealiifano had put the hosts ahead on three minutes when George Smith had the ball pinched illegally in contact by prop Coenie Oosthuizen. However, the centre would go on to have an off-colour first-half from the tee as did opposing kicker Smit, who missed an effort on ten minutes.
What followed was continued Brumbies ball but such is the threat of this ever improving Cheetahs outfit that they scored with their first attacking opportunity. It came from Jesse Mogg putting the ball out on the full and from the line-out, Raymond Rhule broke through before finding Johann Sadie. Sadie's finish wide on the right led to Smit missing the extra two points so it was now 3-5 in what was already an absorbing play-off quarter-final.
Lealiifano would join Smit in having trouble in the swirling wind as he was off-target from the tee on 20 minutes, wayward from 40 out and he would miss again three minutes later after Lappies Labuschagne was adjudged to be offside at a line-out. The growing feeling was one of them would rue their misses and that proved to be the case at full-time.
The Brumbies centre would stop his personal rot before the half-hour when Sadie was offside close to his own line, pushing the hosts ahead by one point. And despite the Cheetahs throwing the kitchen sink at their hosts before the Brumbies hit back late on.
6-5 was how things stayed going into the break.
The Cheetahs would retake the lead on 45 minutes when Heinrich Brussow's excellent work at the breakdown allowed Smit to send over three points. However, Smith would be penalised soon after at the ruck so their lead was short-lived as Nic White made it 9-8.
A scrum offence would take the scores up to 12-8 thanks to Lealiifano's effort from the tee and when the Wallaby made it a seven-point ball game with twelve minutes remaining, it suddenly became now or never for the Cheetahs as the tension became palpable.
The South Africans had ample opportunities to win the game - declining shots at goal to instead go for levelling matters first - and it looked to have paid off when replacement Benjamin crossed on the left touchline following a concerted period of pressure.
However, Smit's kick struck the post to spark mass celebrations in the home camp as they head to Pretoria, with the Cheetahs flying back to the Republic with their tournament over.
Pen: Lealiifano 4, White
Tries: Sadie, Benjamin
Brumbies: 15 Jesse Mogg, 14 Henry Speight, 13 Tevita Kuridrani, 12 Christian Lealiifano, 11 Clyde Rathbone, 10 Matt Toomua, 9 Nic White, 8 Ben Mowen (c), 7 George Smith, 6 Peter Kimlin, 5 Sam Carter, 4 Scott Fardy, 3 Ben Alexander, 2 Stephen Moore, 1 Scott Sio.
Replacements: 16 Siliva Siliva, 17 Ruan Smith, 18 Fotu Auelua, 19 Colby Faingaa, 20 Ian Prior, 21 Andrew Smith, 22 Joe Tomane.
Cheetahs: 15 Hennie Daniller, 14 Willie le Roux, 13 Johann Sadie, 12 Robert Ebersohn, 11 Raymond Rhule, 10 Riaan Smit, 9 Piet van Zyl, 8 Philip van der Walt, 7 Lappies Labuschagne, 6 Heinrich Brussow, 5 Ligtoring Landman, 4 Lood de Jager, 3 Lourens Adriaanse, 2 Adriaan Strauss (captain), 1 Coenie Oosthuizen.
Replacements: 16 Ryno Barnes, 17 Trevor Nyakane, 18 Waltie Vermeulen, 19 Boom Prinsloo, 20 Sarel Pretorius, 21 Elgar Watts, 22 Rayno Benjamin.
Referee: Glen Jackson (New Zealand)
Assistant referees: Rohan Hoffmann (Australia), James Leckie (Australia)
Television match official: Matt Goddard (Australia)